This type of interface may be considered as being relatively restricting in various applications, e.g. identifying people or controlling the access of particular people to a building. It may also be restricting in banking transactions that require the card to pass through a slot in the terminal.
That is why the applicant seeks to provide a remote data interchange system suitable for use over different distances.
The person skilled in the art knows that the amplitude of an electromagnetic signal applied to the terminals of an inductive frame can be varied by coupling the frame inductively with a resonant circuit which is tuned to the frequency of the signal. Such variations are significant when the ratio between the area of the inductive elements of the resonant circuit and the area of the frame is not too great.
However, it is intended, particularly for remote banking transactions, that the bearer of a memory card fitted with a resonant circuit should pass through an inductive frame or "gate" and that information should be exchanged as the bearer is passing through. Unfortunately, the ratio of the area of such a gate (about 1.6 m.sup.2) to the area of a standard memory card (about 40 cm.sup.2) would give rise to amplitude variations which are too small to be indicative of the presence of a card in the gate, and which could possible be interpreted as "noise". In addition, these variations depend on the physical characteristics (e.g. volume) of the person present in the gate, which means that the variations are insufficiently stable to ensure adequate reliability for information interchange during banking transactions, for example.
The invention seeks to provide a solution to this problem.
An object of the invention is to cause an electromagnetic signal at the terminals of an inductive frame or "gate" to vary during remote inductive coupling with a portable object such as a memory card in a manner which is indicative of the presence of the card in the gate.
Another object of the invention is to escape from interfering variations due, in particular, to the physical characteristics of the people carrying such memory cards.
Another object of the invention is to ensure that information is transmitted reliably between the portable object and the station.
Another important object of the invention is to enable remote two-way interchange to take place between the portable object and the station.
The invention also seeks to provide a device which consumes practically no energy when transmitting or when receiving information, and which does so at very low cost.